Over the past thirty years flexible intermediate bulk containers, commonly known as bulk bags, have come into widespread use for receiving, storing, transporting, and discharging flowable materials of all types. Although circular bulk bags are known, bulk bags are typically constructed from rectangular panels which are sewn together along their adjacent edges to define a bulk bag which is initially square or rectangular in horizontal cross section. Nevertheless, all bulk bags, whether initially square, rectangular, or circular in cross section tend to assume a circular configuration when filled due to the uniform pressure imposed by the contents of the bulk bag against the flexible fabric side walls thereof.
U.S. Pat. No. 4,903,859 discloses a bulk bag comprising four double layer side walls. Stiffeners formed from cardboard are inserted between the layers of the side walls thereby imparting sufficient rigidity to the container to permit its use with liquids. Although the bulk bag of the '859 patent has been generally well received, its utilization has been somewhat limited by the fact that it cannot be stacked.
Co-pending application Ser. No. 09/390,403 assigned to the assignee hereof (doing business as Composite Container Corp.) discloses an improvement over the bulk bag of the '859 patent. In application Ser. No. 09/390,403 there is disclosed a bulk bag having double layer side walls and vertically extending corner pockets. Plywood sheets are received between the layers of the side walls and wooden posts are received in the corner pockets to provide a bulk bag suitable for use with liquids which is stackable.
U.S. Pat. No. 5,076,710 discloses a baffle-type bulk bag wherein bridge panels or baffles are sewn across the four corners of a nominally rectangular bulk bag. The baffles prevent the side walls of the bulk bags from bulging outwardly when the bulk bag is filled, thereby retaining the filled bulk bag in a more or less rectangular cross-sectional configuration. The baffles may be provided with apertures which allow material to flow into and out of the corners of the bulk bag during filling and discharging operations.
The present invention comprises an improvement over the prior art as defined by the '859 and '710 patents and application Ser. No. 09/340,403 to provide a baffle-type bulk bag which is stackable. In accordance with the broader aspects of the invention, triangular stiffeners are provided in the triangular corners of baffle-type bulk bags. The stiffeners may be formed from various materials including plastic panels, panels formed from corrugated paperboard and similar materials, etc. The stiffeners may be provided with apertures aligned with the apertures of the baffles thereby permitting the flow of material into and out of the bulk bag during filling and discharging operations.
In accordance with another aspect of the invention, baffle-type bulk bags may be provided with double layer side walls extending between the baffles. In such instances stiffeners may be employed in the side walls of the bulk bag in addition to the stiffeners that are utilized in the triangular corners defined by the baffles.
In accordance with yet another aspect of the invention, there is provided an eight piece bulk bag side wall construction. An outer layer comprises four rectangular sections which are joined along seams disposed at the midpoints of the side walls of the bulk bag. An inner layer also comprises four sections which are similarly joined by seams located at the midpoints of the bulk bag side walls. The inner and outer layers are in turn joined by vertically extended seams located adjacent the corners of the bulk bag thereby defining the baffles and the double layer side walls of the bulk bag.